Millennial men more likely to stray when their wives earn the pay

When it comes to making money, Millennial women are on the move. The wealthy ones are likely to make as much as their husbands, if not more. About 30% are the major breadwinners at home, while another 21% make as much as their husbands. But apparently no gender-gap-bridging deed goes unpunished.

A new study published by the American Sociological Association, suggests that men — and, to a lesser extent, women — are far more likely to cheat when they are economically-dependent on a mate, at least when the subjects are Millennials. Contrary to some popular assumptions, the most stable family relationships happen in an atmosphere of equality, not a traditional role of a male breadwinner and stay-at-home wife and mother.

The paper compared the likelihood of married people age 18 to 32 cheating on their spouses with the percentage of the household income they contributed. Of men who were completely financially dependent on their wives, 15% had an affair, compared to 5% of women. The numbers dropped as household income became even, at which point 3.4% of each cheated.

At that point the behavior by gender significantly diverged. The greater the portion of household income women earned, the less likely they were to cheat, with only 1.5 percent of women who were the complete breadwinners having an extramarital affair. However, as men brought in a larger portion of the total income, the chance of their cheating increased, to 4% of those who brought home all the money.

The study, called Her Support, His Support: Money, Masculinity, and Marital Infidelity looked at an ongoing source of data from the National Longitudinal Survey of Youth, which has tracked people since 1997. Author, Christin L. Munsch, an assistant professor of sociology at the University of Connecticut, told Fortune that the idea came years ago when several couples in her group of friends split up.

“I was speaking with one of the young men and said, ‘Why did you cheat on her?'” Munsch said. “He said, ‘She had all the money and all the friends. I felt completely emasculated. I wasn’t happy in that relationship.’ I thought, ‘Wow, that’s really interesting.'”

Munsch looked across years at the number of sexual partners people reported and their marital status as well to determine whether they must have had sex outside their marriage. With fidelity as one proxy to satisfaction with a relationship she found that neither men nor women are happy being economically dependent on a partner. “But for men there’s something even worse about it,” she said. “That’s because we tell men they’re supposed to be breadwinners.” Munsch thought that male dissatisfaction channels into “masculine overcompensation,” through which men try to reestablish an expected gender role.

As men provide more of the family’s income, they are more likely again to cheat. Munsch thought that opportunity may be the reason. “These men are probably in fairly powerful positions,” she said. That could mean travel, resources to hide infidelity, “and they have more people interested in having sex with them [because of their position and standing].”

Although women who were in the upper economic bracket also likely had similar powerful positions, there are some differences. “We don’t see men throwing themselves at very successful women in the same way,” Munsch said. “Women [also] go to extreme lengths in this situation to shore up their husband’s masculinity. Because we know that women go to these lengths to keep their potentially strained relationships intact, they probably aren’t going to cheat.”

Munsch’s conclusion? The most stable family relationships happen in an atmosphere of equality, not a traditional role of a male breadwinner and stay-at-home wife and mother. Munsch, however, also said that people shouldn’t draw alarmist conclusions if their spouse earns more. “They still only have a 15% chance of engaging in infidelity even when completely dependent on their wives,” she said. “I don’t want people to think ‘Oh my God, my husband is going to cheat on me because he’s dependent!’ We’re probably talking about a specific type of man who buys into a very traditional gender ideology.”